Fleas (Siphonaptera)
The information on the average numbers of fleas on voles was obtained from live-trapped and some snap-trapped voles. Fleas were counted only on voles which were removed from the traps within twenty-four hours after the traps had been last examined. The average numbers of fleas found on prairie voles in this study are given in table 4.
Table 4. Average Numbers of Fleas on Prairie Voles[C]
| Subadults | Adults | |
|---|---|---|
| Live-trapped voles | 1.9 (73) | 3.4 (29) |
| Snap-trapped voles | 1.1 (26) | 1.3 (27) |
[C] The fleas on the live-trapped voles are all Ctenophthalmus pseudagyrtes Baker, and those on snap-trapped voles represent several species (see [table 2]). The numbers in parentheses are the numbers of voles examined.
[Table 5] shows the average degree of infestation for ten months of an eleven month period. The monthly averages for the most part show no variations. The latter half of February provides an exception in that a series of 22 snap-trapped voles and 11 live-trapped voles taken at that time had on the average, 9.7 and 5.3 fleas respectively. Pine mice (Pitymys nemoralis) occurred in small numbers in the area where Microtus ochrogaster was live-trapped, and Ctenophthalmus pseudagyrtes was the flea found to be common on both of these voles.
Table 5.—Monthly Averages of Fleas on Prairie Voles
| Jan. | Feb. | Mar. | Apr. | May | June | July | Aug. | Sept. | Oct. | Nov. | Dec. |
|---|---|---|---|---|---|---|---|---|---|---|---|
| .6 | 5.1 | 5[D] | ... | 3 | 1.8 | 1.4 | 1.7 | ... | 1.1 | 2 | 2 |
| (6) | (11) | (6) | ... | (6) | (88) | (26) | (6) | ... | (8) | (14) | (2) |
[D] This figure is high because one vole had the high number of 19 fleas. The numbers in parentheses show the number of live voles examined for each month. All fleas were Ctenophthalmus pseudagyrtes Baker.
Some fleas have a habitat preference as well as a host specificity. As voles from different areas were examined, different kinds of fleas were encountered. A population of free-living voles under observation on the Campus at Lawrence was parasitized only by Ctenophthalmus pseudagyrtes. From 90 prairie voles collected in a field of clover 4 miles northwest of Lawrence, the only species of flea recovered was Orchopeas leucopus. In both places the prairie vole was the most common mammal, but in the field of clover three deer mice (P. maniculatus) also were trapped. In a third field, one mile west of Lawrence, the prairie vole was host to both the above mentioned fleas. Here both the prairie vole and the cotton rat (Sigmodon hispidus) were common.
The host distribution of fleas on seven small mammals which lived in the same habitats as the prairie vole is given in table 6.
Table 6.—Frequency of Occurrence of Fleas on Seven Species of Small Mammals[E]
Column headings:
A: Cryptotis parva
B: Blarina brevicauda
C: Peromyscus maniculatus
D: Peromyscus leucopus
E: Sigmodon hispidus
F: Microtus ochrogaster
G: Pitymys nemoralis
| A | B | C | D | E | F | G | |
| Orchopeas leucopus (Baker) | 0 | 0 | 53 | 31 | 37 | 6 | 10 |
| Orchopeas howardii (Baker) = | |||||||
| O. wickhami (Baker) | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Nosopsyllus fasciatus (Bosc) | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Epitedia wenmanni (Rothschild) | 0 | 0 | 0 | 9 | 0 | 2 | 0 |
| Rectofrontia fraterna (Baker) | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Corrodopsylla hamiltoni (Traub) | 47 | 8 | 0 | 0 | 0 | 0 | 0 |
| Ctenophthalmus pseudagyrtes Baker | 0 | 38 | 0 | 0 | 4 | 25 | 53 |
| Peromyscopsylla scotti I. Fox | 0 | 0 | 0 | 6 | 0 | 0 | 0 |
| —————————————— | |||||||
|---|---|---|---|---|---|---|---|
| Total number examined | 34 | 13 | 34 | 35 | 57 | 414 | 21 |
[E] The numbers represent the percentage of each species which was parasitized by fleas. The mammals were collected at Lawrence, Douglas County, Kansas, between October, 1945, and June, 1946. These data are entirely from snap-trapped animals with the exception of those from Microtus and Pitymys which are from both snap-trapped and live-trapped animals.
It is seen that some fleas are rather specific in their choice of hosts, and that others are commonly found on two or more small mammals in the same habitat. In each of these groups there are fleas which have a habitat preference, that is to say, the flea lives on the host when the host lives in a given habitat, but is absent when the host lives in another habitat.
Group 1: Fleas with a Host Preference
Epitedia wenmanni was found on the white-footed mouse (Peromyscus leucopus) and only rarely on the prairie vole. Corrodopsylla hamiltoni was taken only from the two kinds of shrews (Blarina brevicauda and Cryptotis parva). Fleas on shrews may have a well-developed host preference. At any rate, Elton, Baker, Ford, and Gardner (1931) found that Doratopsylla dasycnemus rarely strayed from its normal host (Sorex araneus) to other small mammals. Peromyscopsylla scotti was taken from the white-footed mouse (Peromyscus leucopus), and had a habitat preference also. It was found only on those white-footed mice which were trapped in the woodlands at various places in Douglas County; white-footed mice which were trapped in areas of brush were free of this parasite.
Group 2: Fleas Commonly Found on Two or More Kinds of Small Mammals
Orchopeas leucopus was an outstanding example of this group. It was the most common flea on the deer mouse, the white-footed mouse, and the cotton rat. In certain areas it was common on the two voles (Pitymys nemoralis and Microtus ochrogaster). Ctenophthalmus pseudagyrtes is the most abundant flea on the two kinds of voles and on the large shrew (Blarina brevicauda), and was found sparingly on the cotton rat.
Several kinds of fleas do not belong in either of the above groups. Some fleas were accidental strays from mammals not included in [table 6]; and one flea (Rectofrontia fraterna) may prove to be a common nest parasite. Orchopeas howardii is common on tree squirrels (Sciurus niger and S. carolinensis). Nosopsyllus fasciatus is a cosmopolitan flea on Rattus norvegicus. Rectofrontia fraterna was taken once from a prairie vole. Since the only specimens in the University of Kansas Entomological Collections are from "mouse nests," this flea may be found to be a nest inhabiting parasite.
Some fleas are possible bridges by which a blood parasite could be transmitted from one kind of a mammal to another. If Ctenophthalmus pseudagyrtes acted as the intermediate host of a disease-causing organism, an epizootic from Microtus ochrogaster might be transmitted to Pitymys nemoralis or to Sigmodon hispidus or Blarina brevicauda. There are several other such potential bridges for blood parasites. Although [table 6] does not prove that individual fleas wander from one host to another, the frequency with which the several kinds of fleas are removed from live mice suggests that the fleas occasionally do so.